Image forming apparatuses include copiers, printers, facsimiles, multi-function devices thereof, etc. Some image forming apparatuses form a color image on a recording member according to an electrophotographic method. Such an image forming apparatus employing an electrophotographic method includes an image carrier, a charger, an optical writing unit, a developer, and a cleaner.
The image carrier is configured to be a drum shaped or belt shaped photoconductor. On starting an image forming operation, the photoconductor is rotated, and a surface of the photoconductor is charged with the charger. Then, the optical writing unit emits light to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is visualized with toner in the developer.
Further, the resultant toner image is directly transferred onto a recording medium, such as a paper sheet, an OHP film, etc. Alternatively, the resultant toner image is indirectly transferred onto the recording medium via an intermediate transfer belt. Thus, a desired color image is formed on the recording medium.
Such an image forming apparatus may include a process cartridge that is integrally formed with the photoconductor and at least one unit from among the developer, the cleaner, the charger, etc. The process cartridge is configured to be detachably mounted on the main body of the image forming apparatus in order to downsize the image forming apparatus and obtain a high operability in maintenance operation thereof.
In the process cartridge, the developer, the cleaner, or the charger may be configured as a sub unit thereof. In this case, the sub unit is detachably mounted on the process cartridge at a position proximate the photoconductor. Then, the process cartridge including the sub unit is installed in the main body of the image forming apparatus. Thus, a drive force of a driving device provided in the main body of the image forming apparatus is transmitted so as to drive the process cartridge.
Specifically, when the process cartridge is mounted on the main body of the image forming apparatus, a drive shaft of the driving device is connected to a driven shaft of a rotational member in the sub unit, such as a developing roller in the developer unit, a cleaning member in the cleaner unit, or a charging roller in the charger unit. Thus, the image carrier becomes rotatable in conjunction with the developing roller, the cleaning member, or the charging roller.
However, in the main body of the image forming apparatus or the process cartridge, accumulation of dimensional tolerances may cause a positional variation of the drive shaft or the driven shaft. Thus, a relative displacement in axial center may be caused between the drive shaft and the driven shaft.
Further, the relative displacement in axial center between the drive shaft and the driven shaft may cause a variation in rotational torque, thereby resulting in an uneven rotation. Thus, image degradation, such as uneven density or banding, may be caused.
Some image forming apparatuses are configured to have a clearance between the drive shaft provided in the main body of the image forming apparatus and the driven shaft provided in the process cartridge in order to suppress the relative displacement in axial center between the drive shaft and the driven shaft. In such image forming apparatuses, the driven shaft may be configured as a primary guide member to guide the process cartridge into the main body of the image forming apparatus at the installation thereof.
However, for such image forming apparatuses, an effective suppression is still demanded with respect to the relative displacement in axial center between the drive shaft and the driven shaft.